1. Technical Field
The present invention relates to electronic component-mounted structures; methods for mounting electronic components; electro-optical devices, such as liquid crystal devices and light-emitting devices, e.g., organic electro-luminescence (EL) devices, and inorganic EL devices; and electronic apparatuses.
2. Related Art
In circuit boards and liquid crystal display devices mounted on various types of electronic apparatuses, techniques for mounting electronic components, such as semiconductor ICs, are used. For example, in a liquid crystal display device, an IC chip for driving liquid crystal, which drives a liquid crystal panel, is mounted. The IC chip for driving liquid crystal may be directly mounted on a glass substrate constituting the liquid crystal panel or may be mounted on a flexible printed circuit board (FPC). The former mounting structure is referred to as a chip on glass (COG) structure and the latter mounting structure is referred to as a chip on FPC (COF) structure.
When a liquid crystal display device having a COG structure is fabricated, as shown in FIG. 12, an IC chip is mounted using an anisotropic conductive film (ACF) 22 in which conductive particles 22a are dispersed in a thermosetting resin 22b. That is, first, an IC chip for driving liquid crystal 21 is disposed on connecting terminals 11bx and 11dx arranged on a glass substrate 11 with the anisotropic conductive film 22 therebetween. Subsequently, the IC chip 21 is pressed to the glass substrate 11 so that metal bump electrodes 21B are brought into conductive contact with the connecting terminals 11bx and 11dx through the conductive particles 22a. Furthermore, the IC chip 21 is heated to cure the thermosetting resin 22b so that the conductive contact between the metal bump electrodes 21B and the connecting terminals 11bx and 11dx is maintained.
In order to enhance reliability of electrical connection between the metal bump electrodes 21B of the IC chip 21 for driving liquid crystal and the connecting terminals 11bx and 11dx disposed on the glass substrate 11, the intervening conductive particles 22a are required to be elastically deformed by pressure. In such a case, even if the height of the thermosetting resin 22b is changed due to a change in temperature, the conductive contact through the conductive particles 22a can be maintained. However, the conductive particles 22a having a small particle size have high rigidity and it is difficult to secure elastic deformation of the conductive particles 22a that is sufficient for improving reliability of electrical connection. Under these circumstances, as a method of enhancing reliability of conductive connection, use of conductive particles composed of conductive rubber has been known. For example, refer to Japanese Unexamined Patent Application Publication No. 5-182516.
However, recently, with higher resolution and increased color display with respect to liquid crystal display devices, the pitches of the metal bump electrodes 21B and the connecting terminals 11bx and 11dx have been decreasing. As a result, in order to prevent short-circuiting between adjacent electrodes or adjacent terminals, the particle size of the conductive particles 22a must be further decreased. Consequently, the cost of the anisotropic conductive film 22 has increased, resulting in an increase in production cost. It has also become more difficult to secure sufficient elastic deformation of the conductive particles 22a, resulting in a difficulty in securing reliability of electrical connection against a change in temperature. Additionally, in the method in which conductive particles composed of conductive rubber are used, it is still more difficult to decrease the particle size.